1. Field of the Invention
The invention relates to an electrode device for active medical implants.
2. Description of the Related Art
The background of the invention is that the subject matter of the invention is relevant primarily in conjunction with cardiac pacemakers, implantable defibrillators, and other types of active implantable electromedical devices. The latter typically comprise at least one current/voltage-carrying supply lead in the electrode device—which is typically referred to simply as an “electrode”—, the distal end of which is located e.g. in a ventricle and is used to measure cardiological potential signals or to transmit relevant therapeutic current signals.
In the case of implantable electromedical devices, the compatibility of such electrode devices with high-frequency magnetic fields of the type used in imaging diagnostic methods in particular which are based on magnetic resonance—so-called MRI (magnetic resonance imaging) methods—is a serious problem. In such MRI methods, a magnetic alternating field pulsed with radio frequency (RF) is superimposed on a strong static magnetic field, the former being used to change the energy state of the protons in the tissue being investigated and produce MRI signals from the tissue.
Due to the laws of electromagnetic induction, this magnetic alternating field induces alternating voltages in the supply lead of the electrode devices—under discussion here—of electromedical device implants; the energy of the alternating voltages is converted to heat in particular at the electrically conductive contact poles of the electrode device with human tissue. This can result in considerable heating e.g. of the tip contact of a cardiac electrode, thereby impairing or even damaging the surrounding cardiac tissue or cardiac tissue in contact therewith.
To prevent these problems, U.S. Pat. No. 7,363,090 B2 proposes the use of filters on the basis of oscillating circuits composed of a coil in parallel with a capacitor, which is assigned to the corresponding supply lead for the tip contact pole or a ring contact pole of a corresponding electrode of an implantable electromedical device. The filters disclosed in this known patent are designed in practical application by the patent owner as relatively bulky components that reinforce the electrode device along a certain length and impart unfavorable mechanical properties to the electrode equipped therewith. Furthermore, the filter is accommodated in a closed housing that does not provide passage for the guide wires that are typically used when implanting an electrode. The potential uses of this known electrode having a filter device are therefore limited.
US 2009/0281592 A1 makes known filtering components for reducing heating of pacemaker electrodes of an electromedical implant caused by the effect of high-frequency magnetic fields produced during MRI procedures, in which case an induction coil is provided around a non-conductive central portion of a shaft that interconnects a tip contact pole to an inner coil conductor of the electrode device. By mounting an induction coil on the shaft, inductive signal filtering can be provided so as to reduce electrode tip heating, without requiring the incorporation of a lengthy, bulky inductor along the length of the electrode. Capacitive elements can also be integrated in the shaft to create an LC filter circuit. As an alternative thereto, a so-called “air coil” is disclosed in this publication as an inductive element, in which case the shaft can be omitted.
The filter devices according to the prior art typically result in excessive stiffening of the electrode device along a certain length.